DESCRIPTION: Alterations in transmitter expression occur during normal development and growth and in certain diseased states, yet little is known about the physiological consequences of such changes. The aim of this project is to study the functional significance of changes in neuropeptide expression at the cellular level. Specifically, the function of changes in FLRFamide (Phe-Leu-Arg-Phe- NH2) peptides (FaPs) in an identified motoneuron and its skeletal muscle target will be investigated throughout the lifetime of the moth, Manduca sexta. The experiments proposed test the hypothesis that developmentally regulated changes in FaP expression alter the properties of the muscle thus, permitting stage- specific changes in abdominal tone, movements and ultimately behavior. Metamorphosis of the moth involves a tremendous reorganization of the nervous system to accommodate the changing lifestyles of the animal and is a compelling model system used in these studies. The P.I. has demonstrated that dramatic changes in the expression of Manduca FaPs in identified motoneurons temporally correlate to stage specific changes in movement and tone. FaPs are not detected in motoneurons during embryogenesis, appear gradually during the caterpillar stage, decline during metamorphosis under the influence of the changing ecdysteroid titers, and are absent in the newly emerged adult, even though the motoneuron and muscles persist (Witten and Truman, 1990). These studies will focus on four hypotheses to determine the function of alterations in FaP expression: First, do FaP peptides modulate muscle tension? This a common mode of action for members of this large and diverse peptide family (Greenberg and Price, 1992). Tension measurements, transmembrane potentials and conductance changes of the muscles will be recorded when the peptide is present (caterpillar) and absent (newly emerged adult). The results will be compared to bath application of the synthetic peptides. Next, actions of FaPs on fiber types will be assessed during the metamorphic transition using standard enzyme histochemical assays. Third, the potential "growth factor" actions of FaPs will be assessed since their presence is associated with muscle cell proliferation in vitro. Incorporation of bromo-deoxyuridine (BUdR) will be used as a marker for DNA synthesis and proliferation. If time permits, hormonally manipulated heterochromatic mosaics of the animals will be used to help distinguish FaP from steroid mediated actions on muscle. The results obtained in this model system should provide valuable insights into the functional roles for changes in transmitter expression during development, growth and maturation in more complex vertebrate systems.